![]() The synchrotron x rays, traveling along the horizontal axis, pass through a beryllium entrance window, scattering off the sample and into an area detector. The sample lies at the intersection of the horizontal and vertical rotation axes of the diffractometer ( *), with the surface normal, n ^, pointed along the direction of the transfer arm. 17 and 18, but the new geometry places the sample at a position that allows RHEED and x-ray studies to be conducted simultaneously during MBE growth. 6 It is similar to the one described in Refs. 1, we show a schematic of the oxide MBE system at Sector 33ID of the APS, illustrating its geometry for x-ray diffraction as mounted on a six-circle diffractometer. Consequently, the results of in situ x-ray studies can be analyzed with quantitative methods to understand the growth process, 15,16 whereas RHEED is typically used only qualitatively, either as a thickness monitor or to ensure smooth growth behavior. 12–14 This is unfortunate because the weak interaction is associated with kinematical scattering rather than dynamical scattering. For this reason, the number of in situ growth studies using x rays is far fewer than the number of RHEED studies. Therefore, SXRD is typically performed at a synchrotron, and the MBE system is mounted on a large diffractometer. However, since the interaction between the incoming photons and electrons in the sample is much weaker than that between incoming electrons and sample electrons, 11 many more photons need to be scattered for detection. The position of the spot must be sensitive to the structure of the surface, similar to RHEED. 9,10 Here, one also monitors the intensity of a spot in reciprocal space that oscillates during deposition. We find that during the earliest stages of growth, the RHEED and x-ray signals do not agree with each other, demonstrating that while regular RHEED oscillations may imply high quality growth, the film–substrate interface can undergo significant changes during deposition due to the occurrence of interdiffusion at the growth temperature.Īnother method for monitoring thickness during thin film growth is surface x-ray diffraction (SXRD). We describe the results of such in situ studies on the epitaxial growth of perovskite LaNiO 3 on (La 0.18Sr 0.82)(Al 0.59Ta 0.41)O 3 (001). Importantly, because SXRD and RHEED probe different atomic-scale processes during thin film synthesis, their concomitant use enables the extraction of details concerning growth behavior that one cannot determine from either probe alone. The unique deposition chamber, located at the Advanced Photon Source, allows the preparation of complex oxide samples with monolayer precision and facilitates the formation of direct correlations between in situ x-ray studies and the more prevalent RHEED investigations. We perform in situ synchrotron x-ray ray diffraction (SXRD)/reflection high energy electron diffraction (RHEED) studies on the growth of complex oxide thin films by molecular beam epitaxy. ![]()
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